It is well known in the art of motor vehicle design to provide a differential to enable wheels at opposed ends of an axle to rotate at different speeds, for example to avoid undue tire wear. It is also well known to provide certain vehicles with a locking differential which selectively forces the wheels to rotate at the same speed no matter what the difference in traction, thereby providing a tractive advantage in some circumstances.
Also, inter-axle differentials have been developed for use on vehicles with multiple axles, whereby the differential can be locked and power is transmitted equally to all axles. The locking differential system locks the wheels on an axle, while the inter-axle system locks the multiple axles together thereby forcing the drivetrain to transmit power to all axles equally for maximum traction. In the case of certain vehicles designed for pulling heavy loads, such as a road/rail power unit when in rail operation mode, it is important that the differential and inter-axle locks remain engaged during operation.
Despite the advantages of the selective locking system, it has been determined that in certain circumstances it may be desirable to disengage the locks and later re-engage them, and such disengagement means have become a factory standard addition. For example, in some trucks the inter-axle lock may be designed to automatically disengage in response to a condition such as a low-traction event in which the anti-lock braking system (ABS) initiates, which allows for more effective braking. The lock then re-engages automatically after cessation of the low-traction event.
However, the automatic nature of the lock disengagement is problematic in other contexts. The locks are designed primarily to maximize traction, and an operator hauling a heavy load may therefore wish to have the locks engaged at all times during hauling even when faced with intermittent low-traction events. In the case of snow plows ascending an icy slope, disengagement of the inter-axle lock can reduce adhesion and terminate the ascent, and similar situations have been noted with logging trucks pulling heavy loads on washboard road surfaces. As a further example, it is critical in a road/rail vehicle in rail transport operation mode that traction not be lost when pulling railcars, but it is common to experience traction loss or slippage on a rail that could result in ABS initiation and lock disengagement, and subsequent automatic re-engagement under load can damage the differentials and axles.
What is needed, therefore, is a system and method for selectively bypassing the factory differential lock disengagement means.